io: add a into_std method for tokio's TcpStream

Fixes: #3031

Signed-off-by: Fuyang Liu <liufuyang@users.noreply.github.com>

tokio/src/io/poll_evented.rs

@@ -124,6 +124,16 @@ impl<E: Source> PollEvented<E> {
     pub(crate) fn registration(&self) -> &Registration {
         &self.registration
     }
+
+    /// Deregister the inner io from the registration and returns a Result containing the inner io
+    pub(crate) fn into_inner(mut self) -> io::Result<E> {
+        let mut inner = self
+            .io
+            .take()
+            .ok_or(io::Error::from(io::ErrorKind::NotFound))?;
+        self.registration.deregister(&mut inner)?;
+        Ok(inner)
+    }
 }
 
 feature! {

tokio/src/net/tcp/stream.rs

@@ -9,10 +9,10 @@ use std::fmt;
 use std::io;
 use std::net::{Shutdown, SocketAddr};
 #[cfg(windows)]
-use std::os::windows::io::{AsRawSocket, FromRawSocket};
+use std::os::windows::io::{AsRawSocket, FromRawSocket, IntoRawSocket};
 
 #[cfg(unix)]
-use std::os::unix::io::{AsRawFd, FromRawFd};
+use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd};
 use std::pin::Pin;
 use std::task::{Context, Poll};
 use std::time::Duration;
@@ -184,6 +184,25 @@ impl TcpStream {
         Ok(TcpStream { io })
     }
 
+    /// Turn a `TcpStream` into a `std::net::TcpStream`.
+    pub fn into_std(self) -> io::Result<std::net::TcpStream> {
+        #[cfg(unix)]
+        {
+            self.io
+                .into_inner()
+                .map(|io| io.into_raw_fd())
+                .map(|raw_fd| unsafe { std::net::TcpStream::from_raw_fd(raw_fd) })
+        }
+
+        #[cfg(windows)]
+        {
+            self.io
+                .into_inner()
+                .map(|io| io.into_raw_socket())
+                .map(|raw_socket| unsafe { std::net::TcpStream::from_raw_socket(raw_socket) })
+        }
+    }
+
     /// Returns the local address that this stream is bound to.
     ///
     /// # Examples